Make `(A)Rc`/`Weak` `allocator_api` APIs more consistent #119761

zachs18 · 2024-01-09T04:44:01Z

Make Arc/sync::Weak/Rc/rc::Weak unstable feature(allocator_api) APIs more consistent with other containers (well, Box), and with each other.

fn into_raw_with_allocator for all.
- Pairs with from_raw_in (which already exists on all 4 types).
- Name matches Box::into_raw_with_allocator.
- Associated fns on Rc/Arc, methods on Weaks.
fn allocator for all.
- For Rc/Arc, the existing associated fns are changed to allow unsized pointees.
- For Weaks, methods are added.
Remove where A: Clone bound on (stable) Rc::downcast and downcast_unchecked, (unstable) assume_inits, and some (stable) trait impls
- (Arc::{downcast{,_unchecked}, assume_init} were changed by Fix some Arc allocator leaks #120445)
- downcast(_unchecked) and assume_init semantically should not require cloning the allocator; they are essentially just ((un)checked) pointer casts.
- Remove A: Clone bound from From<Vec<T, A>> for Arc<[T], A> (Rc's already didn't have a A: Clone bound) ~~and TryFrom<Arc<[T], A>> for Arc<[T; N], A>~~ (done by Fix some Arc allocator leaks #120445) (see below for Rc)
Make TryFrom<Rc<[T]>> for Rc<[T; N]> allocator-aware.

This is adding 6¹ new unstable functions, changing the bounds on 6 3 unstable functions, and changing the (unstable) bounds on 7 5 stable functions, so I think it needs at least a libs-api FCP? If it also needs an ACP I can make one. (If the parts of this PR should be split I can do that too.)

@rustbot label +A-allocators +T-libs-api -T-libs

Future PR

As a follow-on to this PR, I plan to make a PR/ACP later to move into_raw(_parts) from Container<_, A: Allocator> to only Container<_, Global> (where Container = Vec/Box/Rc/rc::Weak/Arc/sync::Weak) so that users of non-Global allocators have to explicitly handle the allocator when using into_raw-like APIs.

The current behaviors of stdlib containers are inconsistent with respect to what happens to the allocator when into_raw is called (which does not return the allocator)

Type	`into_raw` currently callable with	behavior of `into_raw`
`Box`	any allocator	allocator is dropped
`Vec`	any allocator	allocator is forgotten
`Arc`/`Rc`/`Weak`	any allocator	allocator is forgotten(Arc) (sync::Weak) (Rc) (rc::Weak)

In my opinion, neither implicitly dropping nor implicitly forgetting the allocator is ideal; dropping it could immediately invalidate the returned pointer, and forgetting it could unintentionally leak memory. My (to-be) proposed solution is to just forbid calling into_raw(_parts) on containers with non-Global allocators, and require calling into_raw_with_allocator(/Vec::into_raw_parts_with_alloc)

Technically 5 new and 1 renamed, since rc::Weak::into_raw_with_allocator is not newly added, as it was modified and renamed from rc::Weak::into_raw_and_alloc. ↩

rustbot · 2024-01-09T04:44:09Z

r? @thomcc

(rustbot has picked a reviewer for you, use r? to override)

zachs18 · 2024-01-09T21:49:14Z

@rustbot label -T-libs

r? rust-lang/libs-api

bors · 2024-01-30T19:28:20Z

☔ The latest upstream changes (presumably #120496) made this pull request unmergeable. Please resolve the merge conflicts.

zachs18 · 2024-02-19T06:50:02Z

@rustbot ready

bors · 2024-04-27T16:07:46Z

☔ The latest upstream changes (presumably #124432) made this pull request unmergeable. Please resolve the merge conflicts.

* Add `into_raw_with_allocator` on `Rc`/`Weak` * Remove `where A: Clone` from `Rc::assume_init`s, `Rc::unwrap_or_clone`, and `Rc::downcast(_unchecked)` * Add `fn allocator(&self)` to `Rc`/`Weak` for all `T: ?Sized` * Make `TryFrom<Rc<[T]>> for Rc<[T; N]>` allocator-aware

…ame collisions

…_clone and From<Vec<T, A>> for Arc<[T], A>

zachs18 · 2024-05-01T04:36:41Z

@BurntSushi Friendly ping (I just realized that the r? libs-api probably didn't send a notification)

BurntSushi · 2024-05-01T11:59:27Z

I'm not really dialed into the allocator work. Can you find someone who is to review this? Maybe @matthieu-m?

BurntSushi · 2024-05-01T12:00:07Z

Alternatively, if this PR can be split up into more digestible chunks, that might help get it reviewed more quickly.

matthieu-m · 2024-05-01T16:18:50Z

@BurntSushi From what I can tell, this PR does not require any Allocator specific knowledge, it doesn't actually even introduce any call Allocator methods (it eliminates calls to clone).

I think any libs member comfortable with API requests can tackle this review without issue.

(I'm neither a libs member, nor am I well-versed in API guidelines)

zachs18 · 2024-05-02T17:34:36Z

I'll probably go ahead and split this into multiple PRs then. I probably won't have time to work on that for a week or so, so I'll leave this open if someone wants to reveiw it until then.

zachs18 · 2024-05-10T19:28:23Z

Split into #124980 and #124981. Later PR will add fn into_raw_with_allocator.

… r=Mark-Simulacrum Relax allocator requirements on some Rc/Arc APIs. Split out from rust-lang#119761 * Remove `A: Clone` bound from `Rc::assume_init`(s), `Rc::downcast`, and `Rc::downcast_unchecked` (`Arc` methods were already relaxed by rust-lang#120445) * Make `From<Rc<[T; N]>> for Rc<[T]>` allocator-aware (`Arc`'s already is). * Remove `A: Clone` from `Rc/Arc::unwrap_or_clone` Internal changes: * Made `Arc::internal_into_inner_with_allocator` method into `Arc::into_inner_with_allocator` associated fn. * Add private `Rc::into_inner_with_allocator` (to match Arc), so other fns don't have to juggle `ManuallyDrop`.

Rollup merge of rust-lang#124981 - zachs18:rc-allocator-generalize-1, r=Mark-Simulacrum Relax allocator requirements on some Rc/Arc APIs. Split out from rust-lang#119761 * Remove `A: Clone` bound from `Rc::assume_init`(s), `Rc::downcast`, and `Rc::downcast_unchecked` (`Arc` methods were already relaxed by rust-lang#120445) * Make `From<Rc<[T; N]>> for Rc<[T]>` allocator-aware (`Arc`'s already is). * Remove `A: Clone` from `Rc/Arc::unwrap_or_clone` Internal changes: * Made `Arc::internal_into_inner_with_allocator` method into `Arc::into_inner_with_allocator` associated fn. * Add private `Rc::into_inner_with_allocator` (to match Arc), so other fns don't have to juggle `ManuallyDrop`.

…-only, r=Mark-Simulacrum Add `fn into_raw_with_allocator` to Rc/Arc/Weak. Split out from rust-lang#119761 Add `fn into_raw_with_allocator` for `Rc`/`rc::Weak`[^1]/`Arc`/`sync::Weak`. * Pairs with `from_raw_in` (which already exists on all 4 types). * Name matches `Box::into_raw_with_allocator`. * Associated fns on `Rc`/`Arc`, methods on `Weak`s. <details> <summary>Future PR/ACP</summary> As a follow-on to this PR, I plan to make a PR/ACP later to move `into_raw(_parts)` from `Container<_, A: Allocator>` to only `Container<_, Global>` (where `Container` = `Vec`/`Box`/`Rc`/`rc::Weak`/`Arc`/`sync::Weak`) so that users of non-`Global` allocators have to explicitly handle the allocator when using `into_raw`-like APIs. The current behaviors of stdlib containers are inconsistent with respect to what happens to the allocator when `into_raw` is called (which does not return the allocator) | Type | `into_raw` currently callable with | behavior of `into_raw`| | --- | --- | --- | | `Box` | any allocator | allocator is [dropped](https://doc.rust-lang.org/nightly/src/alloc/boxed.rs.html#1060) | | `Vec` | any allocator | allocator is [forgotten](https://doc.rust-lang.org/nightly/src/alloc/vec/mod.rs.html#884) | | `Arc`/`Rc`/`Weak` | any allocator | allocator is [forgotten](https://doc.rust-lang.org/src/alloc/sync.rs.html#1487)(Arc) [(sync::Weak)](https://doc.rust-lang.org/src/alloc/sync.rs.html#2726) [(Rc)](https://doc.rust-lang.org/src/alloc/rc.rs.html#1352) [(rc::Weak)](https://doc.rust-lang.org/src/alloc/rc.rs.html#2993) | In my opinion, neither implicitly dropping nor implicitly forgetting the allocator is ideal; dropping it could immediately invalidate the returned pointer, and forgetting it could unintentionally leak memory. My (to-be) proposed solution is to just forbid calling `into_raw(_parts)` on containers with non-`Global` allocators, and require calling `into_raw_with_allocator`(/`Vec::into_raw_parts_with_alloc`) </details> [^1]: Technically, `rc::Weak::into_raw_with_allocator` is not newly added, as it was modified and renamed from `rc::Weak::into_raw_and_alloc`.

Rollup merge of rust-lang#125093 - zachs18:rc-into-raw-with-allocator-only, r=Mark-Simulacrum Add `fn into_raw_with_allocator` to Rc/Arc/Weak. Split out from rust-lang#119761 Add `fn into_raw_with_allocator` for `Rc`/`rc::Weak`[^1]/`Arc`/`sync::Weak`. * Pairs with `from_raw_in` (which already exists on all 4 types). * Name matches `Box::into_raw_with_allocator`. * Associated fns on `Rc`/`Arc`, methods on `Weak`s. <details> <summary>Future PR/ACP</summary> As a follow-on to this PR, I plan to make a PR/ACP later to move `into_raw(_parts)` from `Container<_, A: Allocator>` to only `Container<_, Global>` (where `Container` = `Vec`/`Box`/`Rc`/`rc::Weak`/`Arc`/`sync::Weak`) so that users of non-`Global` allocators have to explicitly handle the allocator when using `into_raw`-like APIs. The current behaviors of stdlib containers are inconsistent with respect to what happens to the allocator when `into_raw` is called (which does not return the allocator) | Type | `into_raw` currently callable with | behavior of `into_raw`| | --- | --- | --- | | `Box` | any allocator | allocator is [dropped](https://doc.rust-lang.org/nightly/src/alloc/boxed.rs.html#1060) | | `Vec` | any allocator | allocator is [forgotten](https://doc.rust-lang.org/nightly/src/alloc/vec/mod.rs.html#884) | | `Arc`/`Rc`/`Weak` | any allocator | allocator is [forgotten](https://doc.rust-lang.org/src/alloc/sync.rs.html#1487)(Arc) [(sync::Weak)](https://doc.rust-lang.org/src/alloc/sync.rs.html#2726) [(Rc)](https://doc.rust-lang.org/src/alloc/rc.rs.html#1352) [(rc::Weak)](https://doc.rust-lang.org/src/alloc/rc.rs.html#2993) | In my opinion, neither implicitly dropping nor implicitly forgetting the allocator is ideal; dropping it could immediately invalidate the returned pointer, and forgetting it could unintentionally leak memory. My (to-be) proposed solution is to just forbid calling `into_raw(_parts)` on containers with non-`Global` allocators, and require calling `into_raw_with_allocator`(/`Vec::into_raw_parts_with_alloc`) </details> [^1]: Technically, `rc::Weak::into_raw_with_allocator` is not newly added, as it was modified and renamed from `rc::Weak::into_raw_and_alloc`.

Generalize `fn allocator` for Rc/Arc. Split out from rust-lang#119761 - For `Rc`/`Arc`, the existing associated `fn`s are changed to allow unsized pointees. - For `Weak`s, new methods are added. `@rustbot` label +A-allocators

Generalize `fn allocator` for Rc/Arc. Split out from rust-lang#119761 - For `Rc`/`Arc`, the existing associated `fn`s are changed to allow unsized pointees. - For `Weak`s, new methods are added. ``@rustbot`` label +A-allocators

Generalize `fn allocator` for Rc/Arc. Split out from rust-lang#119761 - For `Rc`/`Arc`, the existing associated `fn`s are changed to allow unsized pointees. - For `Weak`s, new methods are added. ```@rustbot``` label +A-allocators

Generalize `fn allocator` for Rc/Arc. Split out from rust-lang#119761 - For `Rc`/`Arc`, the existing associated `fn`s are changed to allow unsized pointees. - For `Weak`s, new methods are added. ````@rustbot```` label +A-allocators

Generalize `fn allocator` for Rc/Arc. Split out from rust-lang#119761 - For `Rc`/`Arc`, the existing associated `fn`s are changed to allow unsized pointees. - For `Weak`s, new methods are added. `````@rustbot````` label +A-allocators

Rollup merge of rust-lang#124980 - zachs18:rc-allocator, r=Amanieu Generalize `fn allocator` for Rc/Arc. Split out from rust-lang#119761 - For `Rc`/`Arc`, the existing associated `fn`s are changed to allow unsized pointees. - For `Weak`s, new methods are added. `````@rustbot````` label +A-allocators

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Fix conversions of Box<T, A> to Rc<T, A> or Arc<T, A> to use allocator correctly for dropping the Box #119812

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zachs18 force-pushed the rc-into-raw-with-allocator branch from 2134c8e to c412131 Compare February 10, 2024 05:30

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zachs18 force-pushed the rc-into-raw-with-allocator branch from c3136d9 to d86ce86 Compare April 12, 2024 17:41

zachs18 added 5 commits April 29, 2024 18:08

make internal_into_inner_with_allocator an associated fn to prevent n…

f9d7307

…ame collisions

Move Arc::allocator to T: ?Sized

a2002ec

Add {Arc,Weak}::into_raw_with_allocator

052a140

Add fn sync::Weak::allocator, remove A: Clone bound on Arc::unwrap_or…

f23292a

…_clone and From<Vec<T, A>> for Arc<[T], A>

add (private) Rc::into_inner_with_allocator, and use it where Arc does

9f3dc91

zachs18 force-pushed the rc-into-raw-with-allocator branch from d86ce86 to 9f3dc91 Compare April 29, 2024 23:10

This was referenced May 10, 2024

Generalize fn allocator for Rc/Arc. #124980

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Relax allocator requirements on some Rc/Arc APIs. #124981

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zachs18 closed this May 10, 2024

zachs18 mentioned this pull request May 13, 2024

Add fn into_raw_with_allocator to Rc/Arc/Weak. #125093

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Make `(A)Rc`/`Weak` `allocator_api` APIs more consistent #119761

Make `(A)Rc`/`Weak` `allocator_api` APIs more consistent #119761

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Make (A)Rc/Weak allocator_api APIs more consistent #119761

Make (A)Rc/Weak allocator_api APIs more consistent #119761

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Make `(A)Rc`/`Weak` `allocator_api` APIs more consistent #119761

Make `(A)Rc`/`Weak` `allocator_api` APIs more consistent #119761

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